The present invention relates to an inter-network line level adjustment method and system that compensate for different line levels in different telephone networks.
The telecommunication market gets more and more deregulated. This means that there usually are several active operators having their own telephone networks in a given geographical region. Sometimes a subscriber belonging to one operator wishes to call a subscriber belonging to another operator. In such a case different networks have to be interconnected. However, often networks belonging to different operators have different line (signal) levels. This results in a difference in perceived speech level for inter-network calls as compared to intranetwork calls. Furthermore, this difference in line level also gives performance problems in level sensitive equipment, such as echo cancellers and speech coders.
Reference [1] describes systems for manual line level measurement in a telephone network.
Reference [2] describes an automatic level control system based on line level measurements in a telephone network. This system dynamically adjusts the line level to a desired value. A drawback of such a system is that the line level has to be measured before an adjustment is possible. However, such a measurement will take some time. This implies that during the first few seconds of a call the line level may be either too high or too low before a measurement and a consequent adjustment have been made. This is especially annoying if a call from a rather quiet call is followed by a loud one, or vice versa. In this case the completely inappropriate line level of the previous call will be used as starting point for the new call. A similar problem occurs if a loud talker hands over the phone to a more quiet talker (or vice versa) during a call.
Furthermore, none of these systems distinguishes between intranetwork and inter-network calls. Therefore they are not capable of individually adjusting line levels for inter-network calls.
An object of the present invention is an inter-network line level adjustment method and system that provide individual line level adjustment for inter-network calls.
This object is achieved in accordance with the attached claims.
Briefly, the present invention collects statistical data of line levels associated with calls between a remote and a local network. Based on these data the system adjusts the line level of future calls between the remote and the local network. This procedure has several advantages. For example, it is automatic, adjusts levels immediately at the start of a call, and may be implemented in already existing equipment, such as echo cancellers or speech coders.